1. Field of the Invention
The present invention relates to an S-shaped correction capacitor switching device for an automatic tracking monitor for switching the S-shaped correction capacitors to be connected to a deflection coil of an automatic tracking monitor based on the frequency of a horizontal synchronizing signal. The automatic tracking monitor is a monitor display device which can be used for personal computers of various types being connected to them and is able to cope with various horizontal frequencies.
2. Description of the Prior Art
FIG. 1 is a block diagram showing a conventional S-shaped correction capacitor switching device for an automatic tracking monitor. In the figure: 1 is a deflection coil of an automatic tracking monitor; 2a to 2c are S-shaped correction capacitors to be selectively connected to the deflection coil 1; 3a to 3c are respectively provided corresponding to the S-shaped correction capacitors 2a to 2c and they are switches for setting the connection between the deflection coil 1 and each of these S-shaped correction capacitors; 4 is an analog switch which selects a capacitor out of the S-shaped correction capacitors 2a to 2c to be connected to the deflection coil 1 according to the frequency of a horizontal synchronizing signal and makes one of the switches 3a to 3c ON which corresponds to the selected one out of the S-shaped correction capacitors 2a to 2c.
Next, the explanation on the operation will be given. For the analog switch 4 specified changeover frequencies X and Y (0&lt;X&lt;Y) are set beforehand and when a horizontal synchronizing signal is input, the frequency is compared with these switching frequencies X and Y. In the result, when the frequency of a horizontal synchronizing signal is lower than the switching frequency X, the switch 3a is made ON; when the frequency of a horizontal synchronizing signal is equal to or higher than the switching signal frequency X and lower than Y, the switch 3b is made ON; and when the frequency of a synchronizing signal is equal to or higher than the switching signal frequency Y, the switch 3c is made ON. By this arrangement an optimum capacitor corresponding to the frequency of a horizontal synchronizing signal is selected out of the S-shaped correction capacitors 2a to 2c, and thus the optimum S-shaped correction capacitor is connected to the deflection coil 1.
In this case, for switching frequencies X and Y of the analog switch 4, the frequencies which are not used for any horizontal synchronizing frequency in personal computers are selected and set after survey of horizontal synchronizing frequencies of various personal computers. The capacitance of each of these S-shaped correction capacitors 2a to 2c is decided based on the frequency of a horizontal synchronizing signal which is adopted by the most kinds of personal computers in the corresponding frequency range, that is, in each frequency range, a frequency lower than the switching frequency X, a frequency equal to or higher than X and lower than Y, and a frequency equal to or higher than Y.
The conventional S-shaped correction capacitor switching device for an automatic tracking monitor is constituted as described above, so that in frequency ranges sectioned by the switching frequencies set in the analog switch 4, the capacitances of the S-shaped correction capacitors 2a to 2c are decided corresponding to horizontal synchronizing frequencies adopted by the most kinds of devices; when a personal computer is connected to the monitor having such a switching device, the personal computer having a horizontal synchronizing frequency which does not coincide with one of the frequencies decided in the above-mentioned frequency ranges, there remains some distortion in an image on the monitor; furthermore there is a problem that a slight distortion in the image caused by the dispersion of capacity values among the S-shaped correction capacitors, 2a to 2c, can not be removed.